Update README.md

Author: merbla

README.md

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 # serilog-sinks-splunk
 
-![Build status](https://ci.appveyor.com/api/projects/status/yt40wg34t8oj61al?svg=true)
+[![Build status](https://ci.appveyor.com/api/projects/status/yt40wg34t8oj61al?svg=true)](https://ci.appveyor.com/project/serilog/serilog-sinks-splunk)
 
 A sink for Serilog that writes events to [Splunk](https://splunk.com). Moved from the [main Serilog repository](https://github.com/serilog/serilog) for independent versioning. Published to [NuGet](http://www.nuget.org/packages/serilog.sinks.splunk).